Electrolyte purification in manganese electrowinning



Patented July 27, 1948 ELECTROLYTEPURIFICATION IN MANGA- NESEELECTROWINNING William L. Hammerquist, Knoxville, Tenn., as-

signor to Electro Manganese Corporation, Knoxville, Tenn., a corporationof Delaware No Drawing. Application February 1, 1944,

Serial No. 520,689

10 Claims.

, h ,1 i This invention relates to purification of solutions for use aselectrolytes in the electrodeposition including the electrowinning ofmanganese.

In the electrowinning ofmanganese, electrolytic cells are employed inwhich the electrolyte is divided into catholyte and anolyte. A type ofcell in commercial use at thepresent time contains a plurality ofcatholyte chambers suspended in a tank containing anolyte liquid. Acathode,

in sheet form is suspended in each catholyte chamber and these chambersinclude in their structure permeable diaphragms Whichseparate thecatholyte liquid from the anolyte liquid. The anodes are suspended inthe anolyte liquid in spaced relation to the adjacent diaphragm walls sothat the cell comprises a series of anodes and cathodes alternatelyarranged in a row and separated by the catholyte or diaphragm chambers.

Anolyte containing manganese sulfate, ammonium sulfate, and sulfuricacid is withdrawn from the anolyte chamber and used to extract manganeseore and the extract is then subjected to purification. When purified itbecomes catholyte liquid and is suppliedto the catholyte chamber,Metallic manganese is deposited on the cathodes in the cathode chambers.The cathodes are commonly made in sheet form from a suitable metal oralloy. At the end of a predetermined plating period, the cathodes with adeposit of manganese metal thereon are removed from the cathodechambers, the electrolytic deposit is stripped therefrom, and thecathodes after suitable reconditioning are returned to the cell.

In the catholyte chamber the catholyte is partially depleted of itscontents of manganese. It then passes to the anolyte chamber partly orwholly by diifusion and/or partly by other means of transfer, as, forexample, overflow, and becomes anolyte liquid. There is thus acirculation of liquid from-the anolyte chamber to the catholyte chamberand back to the anolyte chamber, and in the course of this circulationoutside the cell, the anolyte liquid is enriched in manganese by contactwith suitably prepared managenese ore,

or by the addition of the manganese sulfate from a source other thanmanganese ore, and subjected to purification.

It will thus be seen that to the circulating stream outside the cell,there is continuously added a source of manganese, and since suchsources contain substances other than manganese which may be generallyreferred to as impurities,

it will be clear that these impurities are being continuously added tothe circulating stream. Such impurities may include iron, arsenic,antimony, cobalt, nickel, copper, molybdenum, and zinc, and it has beenfound necessary either to remove these impurities completely or .elsereduce them to such small or insignificant proportions that they do notinterfere with the plating process and. the production of suitably pureelectrolytic manganese. The latter in its commercial form must beextremely pure, e. g., oi'the order of 99.95% manganese, and in thisform has a acteristic bright, metallic luster.

It has been discovered that soluble or colloidal silica is an impurity,the removal or, control of,

which is highly desirable because of its adverse elfects on obtainingsatisfactory cathodic deposition. Having arrived at this knowledge,theinvention then proceeds further and appl es" a, remedy, this remedybeing the use of a reagent which is eifective in separating silicafromthe solution intendedfor use as catholyte; at least go to an extentsufficient to prevent the abovemen tioned phenomenon; The reagentwhichhas so far been found best adaptedfor'th purpose" is aluminum sulfate.This occurs in variousiorms, as, for example, the anhydrous salt, or thesalt containing water of crystallization, or in the form ofvariousdouble salts. In accordance with the invention,,an aluminumsulfate reagent is applied to the solution to be purified atapH rangeofabout 5.5 to 7.5. V 1 In the commercial electrowinning process where oreis used as the source of manganese, the latter is extractedwith anolyteat a pH which may be from 1 to 3, after which the pH is raised to about5.5 to 6.5, and air or other suitable oxidizing'agent is employed tooxidize the iron" to the ferric" condition and cause the precipitationthereof, together with any arsenicpantimony, and the like which may;beqpresent'. The iron be treated for the removal-of cobalt and nickel,for which purpose the pH is raised to about 7.2 to "7.5 and treated witha precipitant, e. g; am-

monium sulfide, for cobalt, nickel, and other heavy metals whosesulfides are insoluble at this pH range. Since it as been faunadesirable to effect the aluminum sulfate treatmentl at a pH of about 5.5to about 7.5, this treatment may conveniently be carried out on'theinother liquor after separation of the ironprecipitate and gangueandhaving a pH of about 5.5 to 6.5.

char- Still another variation is to add all or'a part of the aluminumsulfate to the mother liquor after separation of the iron precipitateand gangue at a pH range of about 5.5 to 6.5, and the remainder may beadded after the pH has been increased to about 7.2 to 7.5 preparatory toprecipitating the cobalt, nickel, etc.

It is also possible to add thealu-minum sulfate 4 said solutions andadapt them for use as catholyte.

It is, of course, entirely possible to replenish the manganese contentof the anolyte by enriching it with manganese sulfate obtained from anysuitable'source, and the'invention includes, in general, the treatmentof solutions containing manganese sulfate in order to purify them toobtain catholyte liquid. Whether or not the solution is obtained byextracting ore, it may well contain silica in soluble or colloidal form,that is to say, silica in a highly dispersed condition,

which. existseitherin the form of a true soluat any time prior to ironprecipitation and filtra.

tion, as, for instance, during theore leaching operation. This method,however, is deemed wasteful since aluminum begins to precipitate...as.

hydrous oxide at a pH of 3, and the aluminum thus precipitated amountsof precipitated-iron and gangue cannot perform its function efficiently.To attain maximum efiiciency from the aluminum in removing silicates, itshould be precipitated from thesolution-in the absence of .such foreignmaterials as precipitated iron and gangue and at a pH not lower thanabout 5.5 or higher than about 7.5. Practical .considerationsdo notalways :permit such ideal conditions, and operations may haveto becarried out under less favorable conditions.

The addition of the aluminum sulfate causes the formation of theprecipitate of aluminum hydroxide which has been found effective ineliminating soluble orcolloi-dal silica to a sufficient extent.

Proportions of aluminum sulfate varying from about ,10to parts by weightof anhydrous aluminum sulfate for every one hundred thousand parts byweight of solution, have been found adequate. In general, about twentyto twentyfive pounds of 57 per cent. aluminum sulfate to about tenthousand gallons of solution weighing about ten pounds per gallon, havebeen found suflicient.

However, as shown in column 3 of the table at the' end of thespecification and in the paragraph followingthattabl proportions ofaluminum sulfate-(calculated as anhydrous aluminum sulfate) as high as40.0 20=800 "pounds of aluminum sulfate per 10,000 gallons of solutionmay be used and-since a gallon of said solution weighs 10 pounds, theproportion of said aluminum sulfate maybeas high as 800 pounds per100,000 pounds of said solution. l

The precipitate formed by the addition of the aluminum sulfate may beseparated as such prior to the separation of cobalt, nickel, etc.Preferably, however, theprecipitate of aluminum hydrOXide s f d p or toor concurrently with the sulfide precipitate and the tworemoved at thesame time and by the same means, as, for-example, by filtration. In-somecases treatment of the solution with aluminum sulfate may'occurafterseparation of the cobalt, nickel, etc.

There are, of course, numerous specific Variants ofthe manner of addingthe aluminum sulfate, and all such variants areintended to be included,provided the precipitation occurs within a pH range of about 5.5 to7.5..

' It is-tobe .understood that the invention is not limited to thepurification of solutions obtained by extracting manganese-containing.era with sulfuric acid solutions or with anolyte, andis generallyapplicable to the treatment .oisolutions containing manganese sulfateinorder topurify in the presence of large,

tion. or a colloidal solution, and the invention in its-generic aspectsis directed to treatment of solutions to. separate. the silica of thattype therefrom. While impurities other than silica are commonly presentin solutions for the electrodeposition including the electrowinning ofmanganese, the invention is not in its generic aspects limited totheremoval of silica in conjunction with the elimination of the otherimpurities, e. g., iron, cobalt, and nickel, but, rather, to theremoval-of silica whether or not it may be associated, with otherimpurities. Therefore, any spe-. cificdescription of embodimentsof theinvention which includes the treatment of manganesecontaining ore andthe removal of impurities other than silica, are not to be regarded aslimitations in respect of the generic phase of the invention. It is alsoto be pointed out that in some casesv manganese may be electroplated ina cell not provided with a diaphragm, that is to say, incontradistinction to the process of electrowinning 'of manganesefromsolutions containing manganese salts and/or from manganese-containingores, it is quite possible to carry out a manganese electroplatingprocess in which manganese is deposited asa coating on various objects.I-Iere, also, it is necessary to employ a pure electrolyte, andtheinvention is applicable to the purification of solutions for theelectrodeposition of manganese Whether that deposition be anelectroplating process or an electrowinning process. Therefore, it willbe understood that while the specific description of the invention is interms ofan electrowinning process, that specific description is not tobe regarded as a limitation on the .generic features of the invention.

Atypical example of an embodiment of the invention may be describedasfollows:

Anolyte liquid having a composition of about 10 to 18 grams per liter ofmanganese as manganese sulfate, about to grams per liter of ammoniumsulfate and a pH of about 1 to 2, is withdrawn from the anolyte chamberof a commercial cell employed for the electrowinning of manganese andismixed with manganese ore in a digester, the ore being suitablyconditioned, if necessary (e. g., by the process described in theco-pendingapplication of Elmer M. Wanamaker et-al., Serialv No. 497,352,filed August 4, 1943, now Patent.2,397,824, granted April 2, 194 6),and, as-a-result of agitation with the are, a mixture of ore and extractis obtained, the extract havinga concentration of manganese of about 20to 50 grams per liter. The pH of the extract is-ad justed to about5.5-to 6.5, and airor'other suitable-oxidizing agent is employed tooxidize iron to the-ferric condition and cause precipitation thereofalong with any arsenic, antimony, or thelike which may be present. Theinsoluble gangue and iron precipitate is then separated,

allon, thereis added aluminumsulfate in the proportion of about twelveand one-half pounds, calculated as 57 per cent. aluminum sulfate, foreach ten thousand gallons of solution, which is equivalent to aconcentration of anhydrous aluminum sulfate of about seven andone-eighth pounds per one hundred thousand pounds of solution. Thisaddition may occur at a pH of about 5.5 to about 7.5, a typical pH valuebeing about 6.3 and a typical range being about 6.0 to 6.5. Aprecipitate is formed which is preferably allowed temporarily to remainin suspension. Thereafter the pH of the liquid is raised to about 7.2 toabout 7.5 and an additional twelve and oneshalf. pounds of 57 per cent.aluminum sulfate is added. Thus the total amount of aluminum sulfateadded in the two steps is equivalent -to fourteen and one-quarter poundsof anhydrous aluminum sulfate for each ten thousand gallons of solution.Subsequently a precipitant for cobalt, nickel, etc., e. g., ammoniumsulfide, is

added, precipitating the cobalt, nickel, etc., in

the form of their insoluble sulfides mixed with the aluminum hydroxideprecipitate caused by the addition of the aluminum sulfate. The mixedprecipitate is then removed, as by filtration or other suitable means,and the purified liquid is then in suitable condition for use ascatholyte.

In the preferred embodimentof the invention, sufficient precipitant isused to reduce the content of soluble or colloidal silica to not morethan about 0.001 gram per liter before using the purifled solution ascatholyte. For this purpose the solution to be purified may .be analyzedto determine its content of said soluble or colloidal silica and 'anamount of aluminum sulfate added not less than 4.0 parts by weightofaluminum sulfate (100%) for each part by weight of colloidal and/oroluble silica, or about 7.0 parts by weight of commercial aluminumsulfate containing 57% AJ2(SO4)3.

The following table shows the minimum concentrations of aluminumsulfate, calculated as anhydrous or 100% A12(SO4)3 and expressed asgrams per liter (and pounds per 10,000 gallons of solution), necessaryto precipitate varying concentrations of soluble or colloidal silicaexpressed as grams'per liter: 7

lbs. Ah (S 04): gill, of Soluble g./l. of Al: (S04): per 10,000 galorColloidal calc. as Anhylens of solution Silica drous calc. as

Anhydrous Larger excesses over the minimum proportions of aluminumsulfate above set forth are desirable, e. g., excesses of, say, 2 to 20fold.

What is claimed is:

1. The process of treating a solution to be used as an electrolyte inthe electrodeposition including the electrowinning of manganese, saidsolution containing manganese sulfate, ammonium sulfate and solublesilica, which comprises treating said solution at a pH of about 5.5to'7.5 with aluminum sulfate in the proportion of not less than theelectrolyte is divided into catholyte and anolyte and in which processanolyte liquid is withdrawn from the cell and used to extractmanganese-containing ore to produce an extract which is subjected topurification for use as catholyte, said purification includingprecipitation of the iron, separation of the iron precipitate andgangue, and the production of a solution from which said ironprecipitate and gangue have been separated, said solution containingsoluble silica, the improvement which comprises treating said solutionwith aluminum sulfate in the ratio of not less than four parts by weightOf aluminum sulfate calculated as anhydrous aluminum sulfate for eachpart by weight of soluble silica at a pH of about 5.5 to 75, forming 'aprecipitate,

and separating said precipitate.

3. In the process of manganese electrowinning involving the use of anelectrolytic cell in which the electrolyte is divided into catholyte andanolyte and in which process anolyte liquid is withdrawn from the celland used to extract manganese-containing ore to produce an extract whichis subjected to purification for use as catholyte, said purificationincluding precipita tion of the iron, separation of the iron precipitateand gangue, and the production of a solution from which said ironprecipitate and gangue have the electrolyte is divided into catholyteand 65 anolyte and in which process anolyte liquid is withdrawn from thecell and used to extract manganese-containing ore to produce an extractwhich is subjected to purification for use as catholyte, saidpurification including precipitation of the iron, separation of the ironprecipitate and gangue, and the production of a solution from which saidiron precipitate and gangue have been separated, said solutioncontaining soluble silica, the improvement which comprises treating saidsolution with aluminum sulfate in the ratio of about 10 to 20 parts byweight of aluminum sulfate calculated as anhydrous aluminum sulfate toabout one hundred thousand parts of said solution, adding said aluminumsulfate at a pH of about 5.5 to 6.5, then raising the pH to about 7.2

to 7.5, forming a precipitate, and separating said 7. lyte and in whichprocess anolyte liquid is withdrawn from the cell and'used to extractmanganese-containing ore to produce an extract which is subjected topurification for use as catholyte, said purification includingprecipitation of the iron,.separation of the iron precipitate andgangue, and the production of a solution from which said ironprecipitate and gangue have been separated, said solution containingsoluble silica, the improvement which comprises treating said solutionwith aluminum sulfate in the ratio of about to parts by weight ofaluminum sulfate calculated as anhydrous aluminum sulfate to about onehundred thousand parts of said solution, adding a portion of saidaluminum sulfate at a pH of about 5.5 to 6.5, then raising the pH toabout 7.2 to 7.5 and adding the remainder of the aluminum sulfate,forming a precipitate, and separating the precipitate from the solution.

6. The process of treating a solution to be used as an electrolyte inthe electrodeposition including the electrowinning of manganese, saidsolution containing manganese sulfate, ammonium sulfate and solublesilica, which comprises treating said solution at a pH of about 5.5 to7.5 with aluminum sulfate in the proportion of not less thanfour partsby weight of aluminum sulfate calculated as anhydrous aluminum sulfatefor each part by weight of soluble silica, forming a precipitate;treating said solution with a precipitant for cobalt and nickel withinsaid pH range to precipitate cobalt and nickel, and separating thecombined precipitates.

'7 Process of treating a solution to be used as an electrolyte in theelectrodeposition including the electrowinning of manganese, saidsolution containing manganese sulfate, ammonium sulfate, and soluble'silica, whichcomprises treating said solution at a pH of about 5.5 to7.5 with aluminum sulfate in the proportion of not less than about 4milligrams of aluminum sulfate per liter of said solution (0.40 poundper 10,000 gallons of said solution) for each milligram per liter(0.00001 pound per gallon) of said silica, the said aluminum sulfatebeing calculated as anhydrous aluminum sulfate.

8. Process of treating a solution to be used as an electrolyte in theelectrodeposition including the electrowinning of manganesasaid solutioncontaining manganese, sulfate, ammonium sulfate, soluble silica and thesulfatesof cobalt and nickel, which comprises treating said solution ata pH of about 5.5 to 7.5 wit-haluminum sulfate in the proportion of notless than about 4 milligrams of aluminum sulfate per literof said 50--lution for each milligram per liter of said-silica, the said aluminumsulfate being calculated as anhydrous aluminum sulfate, toform aprecipitate of aluminum hydroxide, adding ammonium -ing said solutionata' pH of about 5.5 to 7.5 with aluminum. sulfate in the proportion ofaboutIO to 800 parts by weight of aluminum sulfate ca'lculated asanhydrous aluminum sulfate to about 100,000 parts by Weight of saidsolution, thereby' forming a silica precipitate, and separating saidprecipitate from said solution.

10. In the process of manganese electrowinning involving the use of anelectrolyticcell in which the electrolyte isdivided into catholyt'e andanolyte and in which process anolyte liquid.

is withdrawn from the cell and used to extract manganese-containing oreto produce an'extract which is subjected to purification for use ascatholyte said purification including precipita tion of the iron,separation of the iron precipitate and gangue, and the production of asolution from which said iron precipitate and gangue have beenseparated, said solution containing soluble silica, the improvementwhich comprises treating said solution with aluminum sulfate in theratio of aboutlO to 800 parts by weight of aluminum sulfate calculatedas anhydrous aluminum sulfate to about,100,000 parts by weight of saidsolution at a pH of about 5.5 to 7.5 and thereafter treating saidsolution with a precipitant for cobalt and nickel within said pH range,forming a precipitate, and separating'saidiprecipitate from saidsolution.

WILLIAM L. I-IAMMERQUIST.

REFERENCES CITED.

The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number Name 7 Date 1,137,005 Jacobson Apr. 27,1915 1,843,006 Stevens et al Jan. 26, 1932 l 1,989,603 Nicoll; Jan. 29',1935 2,266,187 Westby Dec., 16, v1941 2,267,831 Liebknecht Dec. 30, 19412,325,723 Wanamaker et a1. Aug. 3, 1943 2,340,188 Jukkola Jan. 25, 1944OTHER REFERENCES Industrial and Engineering Chemistry, vol. 31, July1939, pp. 859, 860, 861.

Water Works Engineering, Oct. 13,1937, pp.

sulfides of cobalt and"

